Transmission line using a phase splitter for high data rate communication in a computerized tomography system

ABSTRACT

A computerized tomography (CT) system includes a stationary frame, an annular rotating frame and apparatus that includes a phase splitter having an input port coupled to receive a modulated carrier having a relatively wide bandwidth. The phase splitter has first and second output ports for supplying, respectively, first and second modulated carrier constituents having a uniform phase angle differential, such as 180°, between one another while maintaining a uniform amplitude over the bandwidth for the modulated carrier. A transmission line is attached to the rotating frame and is positioned around the annular rotating frame. The transmission line comprises one or more individual segments having first and second conductors respectively coupled to the output ports of the phase splitter to receive the first and second modulated carrier constituents from the phase splitter. A coupler is attached to the stationary frame and is positioned sufficiently near the transmission line for establishing radio coupling therebetween to receive the first and second modulated carrier constituents being applied to any of the individual segments.

RELATED APPLICATIONS

This application is related to patent application Ser. No. 08/407,149(RD-24,212), entitled "Transmission line Using a Power Combiner For HighData Rate Communication In a Computerized Tomography System", filedconcurrently with the present invention, assigned to the same assigneeof the present invention and herein incorporated by reference.

BACKGROUND OF THE INVENTION

The field of the present invention is generally related to computerizedtomography (CT) and, particularly, to a transmission line using anaccurate, wideband phase splitter for high data rate communication in aCT system.

CT systems typically employ a rotating frame or gantry to obtainmultiple x-ray images, or views, at different rotational angles. Eachset of images is referred to in the art as a "slice ". A patient orinanimate object is generally positioned in a central opening of therotating frame on a table which is movable axially, thus enablingrespective slices to be obtained at multiple axial positions as well.Each of the slices obtained is then processed in a computer according topredetermined algorithms to produce enhanced images for diagnostic orinspection purposes.

The rotating frame includes an x-ray source, a detector array andelectronics necessary to generate image data for each view. A set ofstationary electronics is employed for processing raw image data intothe enhanced form. Thus, it is necessary to provide for communication ofthe image data between the rotating frame and a stationary frame of theCT system.

The data rate for communication between the stationary and rotatingframes is an important factor because it is desirable to obtain thedesired views as fast as possible to reduce patient discomfort and/or tomaximize equipment utilization. In current CT systems, a single viewtypically comprises about 800 detector channels with a 16 bitrepresentation for each individual detector channel output (i.e., 12.8Kbits per view) and is typically repeated 1,000 times per second,yielding a net data rate requirement of approximately 13 Megabits persecond (Mbit/sec) for image data alone. Future CT systems capable ofsimultaneously constructing multiple image slices by employing four,eight, or sixteen times as many detector channels will increase the datarate requirement to beyond 150 Mbit/sec for image data alone.

Prior CT systems have employed brushes and slip rings for electricallylinking the rotating frame to the stationary frame. However, in general,CT systems utilizing brushes and slip rings for communications havegenerally suffered from significant limitations in the data rates whichcan be achieved. This is due to the substantial time required topropagate the signals around the circular slip rings. At the desireddata rates, the electrical path length around the rings is anappreciable fraction of a bit period, so that electromagnetic wavespropagating around the rings in opposite directions may arrive at areception point at substantially different times in a bit period,causing garbled reception.

U.S. Pat. No. 5,208,581 issued to A. K. Collins, assigned to theassignee of the present invention and herein incorporated by reference,teaches another type of gantry in which brushes and slip tings areemployed for communication. Although the design of Collins providesrelatively high speed communication between the stationary and rotatingframes, the fact remains that the use of contacting brushes and ringsinherently carries certain disadvantages. For example, the mechanicalcontact between the brushes and tings causes wear which requires suchbrushes and rings to be periodically replaced in order to maintainreliable communication. Furthermore, the slip-ting design of Collinsdoes not support the higher data rams needed for multiple-slice CTsystems.

Other CT systems have employed an optical data link for communicationbetween the stationary and rotating frames. Although an optical datalink design avoids typical drawbacks of slip rings and brushes, suchoptical design requires optics which must be fabricated under tightspecifications and which in operation require substantial Spatialalignment in order to achieve reliable optical coupling along therelatively long circumference of the rotating frame. This leads to highcosts and, thus, it is desirable to provide in a CT system an improvedcommunication link which at a low cost provides reliable high data ratecommunication between the stationary and rotating frames of the CTsystem.

It is further desirable to provide a communication link between thestationary frame and the rotating frame which is robust with respect toelectromagnetic radiation interference such as is typically produced ina hospital environment by cellular telephones, defibrillating devices,surgical saws and even electrical noise produced by any given CT system.Furthermore, it is also desirable to reduce the level of electromagneticenergy which is radiated from such communication link in order to complywith governmental regulations such as regulations imposed by the FederalCommunications Commission and/or foreign governments. As disclosed inU.S. patent application Ser. No. 08/307,120, a transmission line and acoupler or probe provide means for implementing such high data ratecommunication link. As further disclosed in U.S. patent application Ser.No. 08/307,130, a U-shaped structure is effectively employed forsubstantially reducing electromagnetic radiation from the transmissionline while providing a passage which allows for the coupler to readilyaccess the transmission line. Although such U-shaped structureeffectively shields the transmission line, it is desirable to reduceelectromagnetic radiation which escapes or leaks around the coupler. Itis also desirable to reduce sensitivity of the coupler to eternallyproduced electromagnetic energy which can interfere with coupleroperation.

SUMMARY OF THE INVENTION

Generally speaking, the present invention fulfills the foregoing needsby providing in a computerized tomography (CT) system having astationary frame and a generally annular rotating frame, an apparatuscomprising a phase splitter having an input port coupled to receive amodulated carrier having a predetermined bandwidth. The phase splitterhas first and second output ports for supplying, respectively, first andsecond modulated carrier constituents having a substantially uniformphase angle differential, such as about 180°, between one another whilemaintaining a substantially uniform amplitude over the bandwidth for themodulated carrier. A transmission line is attached to the rotating frameand is positioned substantially around the annular rotating frame. Thetransmission line comprises one or more individual segments having firstand second conductors respectively coupled to the output ports of thephase splitter to receive the first and second modulated carrierconstituents from the phase splitter. A coupler is attached to thestationary frame and is positioned sufficiently near the transmissionline for establishing radio coupling therebetween so as to receive thefirst and second modulated carrier constituents being applied to anyindividual segment.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the invention believed to be novel are set forth withparticularity in the appended claims. The invention itself, however,both as to organization and method of operation, together with furtherobjects and advantages thereof, may best be understood by reference tothe following description in conjunction with the accompanying drawingsin which like numbers represent like parts throughout the drawings, andin which:

FIG. 1 is a perspective view of a CT system which employs the presentinvention;

FIG. 2 is an exemplary schematic representation of an apparatusemploying a coupler electromagnetically coupled to a transmission linehaving individual segments driven by a respective phase splitter inaccordance with the present invention;

FIG. 3 is a cross section of a microstrip which can be utilized for thetransmission line and/or coupler in respective exemplary embodiments forthe apparatus of FIG. 2;

FIG. 4 is a simplified circuit model schematic for the phase splitter inaccordance with the present invention;

FIG. 5 is a generally schematic representation which includes respectiveside views of coaxial lines wound to form substantially cylindricalwindings in accordance with one exemplary embodiment for the phasesplitter of FIG. 4;

FIG. 6A is a perspective view of two printed circuit stages inaccordance with another exemplary embodiment for the phase splitter ofFIG. 4, and wherein one of the stages is shown horizontally positionedwhile the other stage is shown vertically positioned;

FIG. 6B is a schematic showing a feedthrough connector in the verticalstage shown in FIG. 6A;

FIG. 6C is a cross-sectional view showing an exemplary electricalconnection between the two printed circuit stages of FIG. 6A; and

FIG. 7 is a plot showing exemplary output signal characteristics of aphase splitter in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, a CT system used to produce images of at least aregion of interest of the human anatomy has a patient table 10 which canbe positioned within the aperture 11 of a generally annular rotatingframe or gantry 15 having a predetermined circumference, e.g., outercircumference 16. A stationary frame 12 is conveniently employed tosupport rotating frame 15. A source of imaging energy 13 whichpreferably produces highly collimated x-rays is mounted on the rotatingframe to one side of its aperture 11, and a detector array 14 is mountedto the other side of the aperture. The rotating frame, together withx-ray source 13 and detector array 14, is revolved about the apertureduring a scan of the patient to obtain x-ray attenuation measurementsfrom many different angles through a range of at least 180° ofrevolution. Detector array 14 may comprise multiple rows each havingabout 800 detector channels along its length. The individual output ofeach channel in detector array 14 is connected to a data acquisitionsystem, DAS (not shown). When sampled, each channel output is convertedby the DAS to, for example, a 16 bit digital value representing X-rayintensity.

The rotating frame further includes additional onboard electronics (notshown) which rotates along with rotating frame 15. The onboardelectronics is essentially a slave to stationary electronics systems 30which is located off rotating frame 15. Stationary electronics systems30 is a computer-based system for issuing commands to the onboardelectronics on rotating frame 15 and for receiving the resulting imagedata, via suitable electrical leads from stationary frame 12, to performprocessing of the received image data.

The present invention is directed to apparatus for high data ratecommunication between the rotating frame and the stationary framethrough the use of a transmission line that is differentially driven byan accurate, wideband phase splitter. The transmission line is, in turn,noncontactively coupled to a probe or coupler. This noncontactivecoupling advantageously avoids the use of slip rings and brushes andallows for continuous rotation of rotating frame 15. As discussed above,multiple-slice CT systems require high data rate communication. Thepresent invention advantageously allows for such high data ratecommunication, (e.g., exceeding 150 Mbits/sec) without the use ofbrushes and slip rings or without the use of costly optical devices.Further, the present invention allows for reliable and cost effectivehigh data rate communication notwithstanding the relatively longcircumference (approximately 13 ft) of the rotating frame.

In the discussion which follows, it is assumed that all of thecommunication between rotating frame 15 and stationary frame 12 has beenserialized, i.e., converted from parallel to serial data fortransmission and vice versa on reception, employing well knownmultiplexing techniques. This is done so that only a single bit streamneed be transmitted, although it should be apparent to those skilled inthe art that multiple parallel paths according to the present inventioncould be employed. In each case, multilevel or multiphase encodingtechniques can be employed to further increase the maximum data rateavailable.

As shown in FIG. 2, a transmission line 40 is attached to rotating frame15 (FIG. 1 ) and is positioned substantially around the rotating frame,for example, around the circumference of the rotating frame. Similarly,the transmission line can be conveniently affixed to the annulus of therotating frame, i.e., the surface bounded by the concentric circles inthe rotating frame; for example, the concentric circle which definesaperture 11 and the larger concentric circle which has circumference 16.Further, it will be appreciated that the present invention need not belimited to circular geometric arrangements since geometric arrangementsother than circular can equally benefit from the present invention.Transmission line 40 comprises one or more segments, such as individualsegments 50 and 60 each having a respective first end 52 and 62 and arespective second end 54 and 64. In FIG. 2, each respective individualsegment is represented by twin lines since, as best seen in FIG. 3, eachof the individual segments includes first and second signal conductorscarrying respective signals being substantially 180° out-of-phase withrespect to one another, that is, each transmission line segment isdifferentially driven by a respective phase splitter, such as phasesplitters 72 and 74. Although two phase splitters are shown in FIG. 2,it will be appreciated that the output signals from a single phasesplitter could be readily split and amplified for effectively drivingindividual transmission line segments 50 and 60; thus, one need not usea separate phase splitter for driving each respective one of theindividual segments. For example, one respective first end of segments50 and 60 could be readily connected in parallel to receive the in-phaseoutput signal of a single phase splitter while the other respectivefirst end of segments 50 and 60 could be connected in parallel toreceive the out-of-phase output signal of the single phase splitter andthus, in this example, only a single phase splitter would be needed fordriving segments 50 and 60. Preferably, each individual segment 50 and60 has a respective electrical length chosen so that a modulated signalapplied at each respective first end 52 and 62 has a predeterminedtime-delay upon arrival at each respective second end 54 and 64. It willbe appreciated that if the respective electrical lengths for segments 50and 60 are substantially similar to one another, the above-describedsegment arrangement results in the modulated signal arriving at eachrespective second end with a substantially similar time delay relativeto one another.

As shown in FIG. 2, a modulated carrier is applied to the respectiveinput ports of phase splitters 72 and 74. The modulated carriertypically has a relatively wide bandwidth, such as from 100 MHz to over1 GHz. The modulated carrier can be conveniently generated by theonboard electronics on rotating frame 15 employing any of a number ofreadily available modulation techniques, such as pulse amplitudemodulation, frequency-shift keying and the like. As shown in FIG. 2,phase splitters 72 and 74 have respective output ports for supplyingrespective output signals, such as respective first and second modulatedcarrier constituents M₁ and M₂ having a substantially uniform phaseangle differential, such as 180°, between one another while maintaininga substantially uniform amplitude over the bandwidth of the modulatedcarrier. As suggested above, each segment receives the respective firstand second modulated carrier constituents which are substantially 180°out-of-phase with respect to one another. Each respective phase splitteroutput port can be optionally connected to matching resistors 76 and 78having a predetermined resistance value selected to match the impedancecharacteristics of the respective transmission line segments. Similarly,each respective second end 54 and 64 is respectively connected totermination resistors 80 and 82 having a predetermined resistance valuechosen to minimize reflection of energy in individual transmission linesegments 50 and 60. Other arrangements may be employed which althoughhaving differences in time delay between individual segments, suchtime-delay differences can be tolerated depending on the specificapplication. For example, phase splitter 74 and matching resistors 78could be respectively connected to each second end 64 in lieu of eachfirst end 62 and termination resistors 82 respectively connected to eachfirst end 62 in lieu of each second end 64. In this case although apredetermined time delay would exist between the individual segments,such time delay could be acceptable in certain applications.

Individual segments 50 and 60 are preferably arranged so that respectivefirst ends of any two consecutive segments are substantially adjacent toone another and respective second ends of any two consecutive segmentsare substantially adjacent to one another. The gap size between any twoconsecutive segments should be small relative to carrier wavelength. Forexample, about 1/8 in. for a 750 MHz carrier. This arrangementconveniently allows for avoiding time-delay discontinuities between anyof the respective individual segments encircling the rotating frame.This also allows for effective coupling operation between thetransmission line and the coupler at all rotation angles. As shown inFIG. 2, each of the two individual segments 50 and 60 can be designed tosubtend a respective angle of about 180° around the circumference of therotating frame. In general, it will be appreciated that a number of Nindividual segments each respectively subtending an angle of about360°/N around the circumference of the rotating frame wherein N is apredetermined even number will be equally effective in alternativeembodiments of the present invention since the modulated differentialsignal (i.e., the net result of the first and second modulated carrierconstituents being substantially 180° out-of-phase with respect to oneanother) in each case is available for reception anywhere along thecircumference of the rotating frame including any gaps between any ofthe N individual segments. As suggested above, there may be applicationswhich can tolerate a predetermined time delay between the individualsegments. In this case, the N number of individual segments need not belimited to an even number since a predetermined odd number of individualsegments could be effectively utilized for applications which toleratesuch predetermined time delay. The foregoing construction for theindividual segments assumes that each segment is made up of a materialhaving a substantially similar dielectric constant. However, it will beapparent that segment materials having predetermined differentdielectric constants can also be conveniently employed. In this case,the angle subtended by each respective individual segment need not beidentical to each other.

The apparatus of the present invention further comprises a coupler 100attached to stationary frame 12 (FIG. 1 ) and being positionedsufficiently near the differentially driven transmission line forestablishing radio coupling therebetween in order to receive the firstand second modulated carrier constituents being applied to theindividual segments. As used herein the expression "radio coupling"refers to noncontactive transfer of energy by electromagnetic radiationat radio frequencies.

It will be appreciated that coupler 100 has a predetermined lengthdimension along a coupler axis 102 which, for example, can besubstantially parallel relative to individual segments 50 and 60. Thecoupler length dimension is conveniently chosen to be sufficiently shortto substantially avoid frequency-dependent directional coupling effects,and to be sufficiently long to avoid substantial signal reduction incoupler 100 whenever the coupler passes about any gap between respectiveones of the individual segments. As indicated by arrows 104 and 106, therespective modulated carrier constituents applied to respective segments50 and 60 propagate in opposite directions and thus to avoid blind spotsnear any of the gaps, coupler 100 preferably has a first end 110directly connected to output port means 112, such as a coaxial line pairor other suitably shielded electrical conductor pair, and has a secondend 108 which is substantially free of any termination impedance, i.e.,termination resistors. In this manner, each modulated carrierconstituent received by coupler 100 passes to coaxial line pair 112independently of the propagation direction of the received modulatedcarrier constituents, i.e., independently of the propagation directionof the respective electromagnetic waves traveling in individual segments50 and 60. For instance, waves arriving at second end 108 readilypropagate toward the first end and from there to coaxial line pair 112,whereas waves arriving at first end 110 are eventually reflected backfrom the resistively unterminated second end 108 toward the first endand from there to coaxial line pair 112. In each case, coupler 100advantageously allows for noncontactively extracting the respective 180°out-of-phase modulated carrier constituents propagating in thetransmission line along the full circumference of the rotating frame. Apower combiner 114 recombines into a single modulated carrier the firstand second modulated carrier constituents being supplied by coupler 100.For additional details about the power combiner the reader is referredto U.S. patent application Ser. No. 08/407,149, (RD-24,212) entitled"Transmission Line Using a Power Combiner For High Data RateCommunication in a Computerized Tomography System", by D. D. Harrison,assigned to the same assignee of the present invention and hereinincorporated by reference. As will be appreciated by those skilled inthe art, the length dimension of the coupler can vary depending on thespecific value of the carrier frequency being utilized for the modulatedsignal. By way of example and not of limitation, the coupler lengthdimension can be chosen in the range of λ/4 to λ/8 wherein λ representsthe wavelength of the carrier in the transmission line material. Otherconfigurations for the coupler will be readily apparent to those skilledin the art.

FIG. 3 illustrates a cross section of a substantially planartransmission line which can be effectively used both for thedifferentially driven transmission line segments and for the coupler.For example, FIG. 3 shows a microstrip 200 wherein substantiallyparallel first and second conductors 202 and 203 and a ground plane 206are separated from one another by a suitable dielectric material 204. Itwill be appreciated that such substantially planar transmission line canbe readily fabricated employing well known printed circuit techniqueswhich allow for substantial savings in cost as compared to an opticaldata link. Similarly, a stripline transmission line wherein the firstand second conductors are "sandwiched" in a respective dielectricmaterial between two ground planes can be alternatively employed bothfor the transmission line segments and for the coupler. Furthermore, thecoupler need not consist of a microstrip or a stripline transmissionline. A suitable conductor, such as a short piece of twin wires, alignedsubstantially parallel to the driven transmission line, will also workeffectively.

FIG. 4 shows a simplified circuit model schematic for an accurate,wideband phase splitter, such as either of phase splitters 72 or 74,used for differentially driving transmission line 40 (FIG. 2). As shownin FIG. 4, the phase splitter comprises a dividing network 300 that canoptionally include first and second matching resistors 302 and 304coupled in parallel to the input port of the phase splitter. Matchingresistors 302 and 304 are optionally employed in dividing network 300being that, depending upon any specific implementation for the phasesplitter, such matching resistors 302 and 304 can be readily eliminated.A first transmission line 306, schematically represented as a delay line307₁ is coupled between first resistor 302 and the first output port ofthe phase splitter for supplying a respective output signal having aphase angle substantially in-phase with respect to the modulated carrierreceived at the input port of the phase splitter. As will be understoodby those skilled in the art, transmission line 306 introduces apredetermined time delay to any signal propagating therethroughdepending upon the electrical length of transmission line 306 and hencethe representation of transmission line 306 as a delay line. The outputsignal supplied by first transmission line 306 is a delayed version ofthe modulated carrier input and constitutes the first modulated carrierconstituent supplied by the phase splitter.

In contrast to first transmission line 306, which as suggested abovesimply introduces the predetermined time delay, without any phaseshifting, to its respective output signal, a second transmission line308 is designed to provide a predetermined level of inductance betweensecond resistor 304 and a predetermined electrical ground. Thus, secondtransmission line 308 is schematically represented as a delay line 307₂in series with an inductor 310, which represents the inductance impartedby transmission line 308 between second resistor 304 and thepredetermined electrical ground. Second transmission line 308 includesreversing means 312 coupled to the second output port for supplying arespective output signal having a phase angle substantially 180°out-of-phase with respect to the modulated carrier. The inductanceprovided by the second transmission line effectively allows reversingmeans 312 to impart the desired 180° phase change to the output signalfrom the second transmission line without electrically shorting suchoutput signal. The output signal supplied by second transmission line308 constitutes the second modulated carrier constituent supplied by thephase shifter. A compensating coil 314 is coupled between the firstoutput port of the phase splitter and the predetermined electricalground. Compensating coil 314 effectively balances the level ofinductance provided by second transmission line 308 so that each of thefirst and second transmission lines 306 and 308 provide a substantiallyidentical impedance to the first and second modulated carrierconstituents respectively propagating therethrough, assuming the firstand second output ports are equally terminated.

It will be appreciated that the respective electrical lengths of thevarious electrical components which make up the phase splitter, such asdividing network 300 and transmission lines 306 and 308, are preferablyselected so that signals which respectively propagate from splittingpoint S to each of the first and second output ports of the phasesplitter have a substantially identical time delay relative to oneanother upon arrival to the first and second output ports of the phasesplitter. Thus, assuming dividing network 300 introduces a substantiallyidentical time delay to signals which propagate from splitting point S,then any time delay introduced, respectively, by the first and secondtransmission lines 306 and 308 should have a substantially identicalvalue to one another. With respect to matching resistors 302 and 304, itwill be appreciated that resistors 302 and 304 could be readilyeliminated if the impedance values for transmission lines 306 and 308were suitably chosen to provide any desired impedance matching betweenthe phase splitter and any circuitry connected to the phase splitter,such as the circuitry (not shown) that generates the modulated carrierbeing supplied to the input port of the phase splitter. For example, ifthe input port has an input impedance of 50 Ohms, and if each oftransmission lines 306 and 308 has a line impedance of 50 Ohms, theneach of matching resistors 302 and 304 would require a value of 50 Ohmsto achieve substantial impedance matching between the input port of thephase splitter and each of the first and second transmission lines. Inthe above example, substantial impedance matching could also be achievedby eliminating matching resistors 302 and 304 and choosing each oftransmission lines 306 and 308 to have a line impedance of 100 Ohms.Further, in some applications substantially accurate impedance matching,such as described above, may not be necessary being that someapplications can readily tolerate a predetermined level of impedancemismatch. Thus, it will be appreciated that any desired impedancematching in the phase splitter can be achieved in many different ways,including even without the use of matching resistors 302 and 304.

FIG. 5 shows one exemplary embodiment for first and second transmissionlines 306 and 308. In this embodiment, transmission lines 306 and 308each comprises a respective coaxial line having a substantially similarelectrical length for maintaining the desired phase differential betweenthe first and second modulated carrier constituents. As best shown inFIG. 5, each of the coaxial lines preferably comprises a flexiblecoaxial line wound to form a substantially cylindrical winding. Thisconfiguration, conveniently allows for circuit symmetry and compactnessand for relatively low electromagnetic interaction between the first andsecond transmission lines. In this embodiment, reversing means 312 isconveniently made up by the outer shield and center conductor of thecoaxial line for the second transmission line, that is, the centerconductor of the coaxial line for the second transmission line iselectrically grounded while the outer shield supplies the out-of-phaseoutput signal. Conversely, the outer shield of the first transmissionline is electrically grounded while the center conductor supplies thein-phase output signal.

FIG. 6A shows another exemplary embodiment for first and secondtransmission lines 306 and 308 (FIG. 4). In this embodiment,transmission lines 306 and 308 comprise a first printed-circuit stage400 including for each of the transmission lines a respective pair ofsubstantially corresponding conductive strips, such as strips 402 and404 disposed on mutually opposite surfaces of a first substrate 406. Asshown in FIG. 6A, transmission lines 306 and 308 further comprise asecond printed-circuit stage 410 including for each of the transmissionlines a respective pair of substantially corresponding coils, such ascoils 412 and 414 each respectively coupled, i.e., electricallyconnected, to a respective one of the conductive strips in the firstprinted circuit stage. Although conductive strips 402 and 404 arerepresented in FIG. 6A by thin lines, it will be appreciated thatconductive strips have a width dimension similar to the width dimensionfor coils 412 and 414. The thin line representation was convenientlychosen for the sake of simplicity of illustration. Further, in FIG. 6,the subindex numeral assigned to each of corresponding strips 402 and404 and to each of corresponding coils 412 and 414 convenientlyidentifies the particular transmission line (of the first and secondtransmission lines) made-up with such strips and coils. For example,coils 412₁, and 414₁, represent the pair of corresponding coils for thefirst transmission line whereas coils 412₂ and 414₂, represent the pairof corresponding coils for the second transmission line. Similarly,strips 402₁ and 404₁ represent the pair of corresponding strips for thefirst transmission line whereas strips 402₂ and 404₂ represent the pairof corresponding strips for the second transmission line.

The electrical connection between printed circuit stages 400 and 410 canbe made at suitable ends of the conductive strips and coils, as bestshown in FIG. 6C for the first transmission line. For example, strip402₁ is connected to coil 412₁ through a respective connectingconductor, such as a conductive joint 422, or a flexible wire and thelike. Similarly, strip 404₁ is connected to coil 414₁ through arespective connecting conductor, such as a conductive pin 420electrically connected to strip 404₁ by way of a suitable conductivejoint 424. As shown in FIG. 6C, the connecting end of coil 414₁ extendsbeyond the connecting end of coil 412₁ to take into account thethickness of substrate 406. It will be appreciated that similarelectrical connections can be made at suitable ends of the strips andcoils for the second transmission line. Similar to conductive strips 402and 404, coils 412 and 414 are disposed on mutually opposite surfaces ofa second substrate 416. Preferably, each of the mutually oppositesurfaces on the second substrate is positioned substantiallyperpendicular relative to the mutually opposite surfaces on the firstsubstrate. This allows for reducing electromagnetic interference betweensignals propagating in the first and second printed circuit stages.Further, the gap spacing between any two adjacent loops of theconcentric loops or turns that respectively make up coils 412 and 414should preferably be sufficiently wide relative to the loop width forreducing electromagnetic crosstalk therebetween. For example, the gapspacing can be readily selected to be about three times as wide as theloop width. Although FIG. 6A shows coils 412 and 414 as havingconcentric loops with comers, i.e., generally rectangular loops, it willbe appreciated that other geometric configurations will also workequally effective for the coil loops. For example, the coil loops couldbe made generally circular and the like, in lieu of generallyrectangular.

In this embodiment, reversing means 312 (FIG. 4) comprises a feedthroughconnector 320, conceptually shown in FIG. 6B. The feedthrough connectoris designed to invert signal flow across each respective one of the pairof substantially corresponding strips for the second transmission line.For example, as conceptually shown in FIG. 6B, feedthrough connector 320allows for inverting signal flow in second transmission line 308 acrossconductive strips 402₂ and 404₂ disposed on the mutually oppositesurfaces of substrate 406, that is, the signal carried by strip 402₂passes through substrate 406 and continues along the surface situatedopposite to the surface where strip 402₂ was located prior to beingspatially inverted or flipped by feedthrough connector 320, while thesignal carried by strip 404₂ passes through substrate 406 and continuesalong the surface situated opposite to the surface where strip 404₂ waslocated prior to being spatially reversed or flipped by feedthroughconnector 320. As will be apparent to those skilled in the art,feedthrough connector 320 is designed to avoid electrically shorting outany signals propagating in the respective conductive strips. It will beappreciated that by using printed circuit stages, a phase splitter inaccordance with the present invention can be readily fabricatedemploying well-known printed circuit techniques which allow forsubstantial savings in cost over other circuit fabrication techniques.Although not explicitly shown in FIG. 6A, it will be appreciated thatmatching resistors 302 and 304 (FIG. 4) and compensating coil 3 14 (FIG.4) can be readily incorporated to the embodiment of FIG. 6 usingwell-known printed circuit techniques. See for example, a paper by C.Brunetti and R. Curtis, entitled "Printed Circuit Techniques", pp.121-159, Proceedings of the I.R.E., Waves and Electrons Sections,January, 1948, for an early but comprehensive treatment of variousprinted circuit techniques. It will also be appreciated that, assuggested above, the respective electrical lengths of transmission lines306 and 308 are preferably chosen substantially identical to one anotherfor maintaining the desired phase differential between the first andsecond modulated carrier constituents.

FIG. 7 is a plot showing exemplary output characteristics for a phasesplitter in accordance with the present invention. In this example, itcan be seen that the phase splitter advantageously provides asubstantially uniform 180° phase differential while providing asubstantially uniform amplitude over the bandwidth of interest. The plotshown in FIG. 7 assumes a flat amplitude input signal swept from 10 to1000 MHz. As shown in FIG. 7, the signal labeled "single output signal"represents an exemplary output signal provided by either one of theoutput ports of the phase splitter while the signal labeled "sum ofoutput signals" represents the sum of the substantially 180°out-of-phase output signals supplied by the phase splitter. As shown inFIG. 7, at least 30 dB of cancellation is obtained in the signalsummation, indicating that the output signals from the phase splitterare in fact of substantially equal amplitude and substantially 180°out-of-phase over the bandwidth of interest.

Although various specific constructions have been given for the presentinvention, it is to be understood that these are for illustrativepurposes only. Various modifications and adaptations will be readilyapparent to those skilled in the art without departing from thesubstance or scope of the invention. For example, although the shieldedtransmission line segments have been described as rotating along withrotating frame or gantry 15 (FIG. 1 ) and the coupler has been describedas attached to stationary frame 12 (FIG. 1 ), it is equally possible toinstead have the shielded transmission line segments stationary and thecoupler mounted on the rotating frame, i.e., stationary and rotatingmechanical mounting for the coupler and transmission line segments canbe readily interchanged with equally effective results. Accordingly, itis intended that the invention be limited only by the spirit and scopeof the claims appended hereto.

What is claimed is:
 1. A computerized tomography system comprising:afirst frame; a second frame relatively rotatable with respect to saidfirst frame; a phase splitter having an input port coupled to receive amodulated carrier having a predetermined bandwidth, said phase splitterhaving first and second output ports for supplying, respectively, firstand second modulated carrier consitituents having a substantiallyuniform 180° phase angle differential between one another whilemaintaining a substantially uniform amplitude over said bandwidth; atransmission line attached to said second frame and positionedsubstantially around said second frame, said transmission linecomprising at least one individual segment having first and secondconductors respectively coupled to the first and second output ports ofsaid phase splitter to receive the first and second modulated carrierconstituents from said phase splitter; and a coupler attached to saidfirst frame and being positioned sufficiently near said transmissionline for establishing radio coupling therebetween so as to receive thefirst and second modulated carrier constituents being applied to said atleast one individual segment.
 2. The computerized tomography system ofclaim 1 wherein said phase splitter comprises:a dividing networkcomprising first and second resistors coupled in parallel to the inputport of said phase splitter; a first transmission line coupled betweensaid first resistor and the first output port of said phase splitter forsupplying a respective output signal having a phase angle substantiallyin-phase with respect to the modulated carrier, the output signalsupplied by said first transmission line constituting the firstmodulated carrier constituent supplied by said phase splitter; and asecond transmission line adapted to provide a predetermined level ofinductance between said second resistor and a predetermined electricalground, said second transmission line including reversing means coupledto the second output port for supplying a respective output signalhaving a phase angle substantially 180° out-of-phase with respect to themodulated carrier, the output signal supplied by said secondtransmission line constituting the second modulated carrier constituentsupplied by said phase splitter.
 3. The computerized tomography systemof claim 2 further comprising a compensating coil coupled between thefirst output port of said phase splitter and said predeterminedelectrical ground.
 4. The computerized tomography system of claim 2wherein said first and second transmission lines each comprises arespective coaxial line having a substantially similar electrical lengthrelative to one another.
 5. The computerized tomography system of claim4 wherein each of said coaxial lines comprises a flexible coaxial linewound to form a substantially cylindrical winding.
 6. The computerizedtomography system of claim 4 wherein said reversing means comprises theouter shield and the center conductor of the coaxial line for saidsecond transmission line, said center conductor being connected to saidpredetermined electrical ground while said outer shield is connected tothe second output port of said phase splitter to supply the secondmodulated carrier constituent.
 7. The computerized tomography system ofclaim 2 wherein said first and second transmission lines comprise afirst printed-circuit stage including a respective pair of substantiallycorresponding conductive strips for each of said transmission lines,respective ones of the conductive strip pairs being disposed on mutuallyopposite surfaces of a first substrate.
 8. The computerized tomographysystem of claim 7 wherein said first and second transmission linesfurther comprise a second printed-circuit stage including a respectivepair of substantially corresponding coils for each of said transmissionlines, each respective one of the coil pairs being coupled to arespective one of the conductive strips in said first stage and beingdisposed on mutually opposite surfaces of a second substrate.
 9. Thecomputerized tomography system of claim 8 wherein each of said mutuallyopposite surfaces on said second substrate is positioned substantiallyperpendicular relative to the mutually opposite surfaces on said firstsubstrate.
 10. The computerized tomography system of claim 7 whereinsaid reversing means comprises a feedthrough connector adapted to invertsignal flow across each respective one of the pair of substantiallycorresponding strips for said second transmission line.
 11. Thecomputerized tomography system of claim 10 wherein said first and secondtransmission lines each has a substantially similar electrical lengthrelative to one another.
 12. The computerized tomography system of claim2 wherein the transmission line attached to said second frame furthercomprises additional individual segments each having respective firstand second conductors coupled to receive respective first and secondmodulated carrier constituents, said at least one segment and saidadditional segments being arranged so that predetermined ends of any twoconsecutive segments are substantially adjacent to one another to avoidtime-delay discontinuity in the modulated carrier constituentspropagating therethrough.
 13. The computerized tomography system ofclaim 12 wherein said coupler comprises a substantially planartransmission line having first and second conductors alignedsubstantially parallel to one another and being respectively positionedsubstantially parallel relative to the first and second conductors ofthe respective individual segments.
 14. The computerized tomographysystem of claim 12 wherein each of said individual segments comprises arespective substantially planar transmission line and each respectivefirst and second conductor in said individuals segments is substantiallyparallel to one another.
 15. In a computerized tomography system havinga first frame and a second frame relatively rotatable with respect tosaid first frame, an apparatus comprising:a phase splitter having aninput port coupled to receive a modulated carrier having a predeterminedbandwidth, said phase splitter having first and second output ports forsupplying, respectively, first and second modulated carrier constituentshaving a substantially uniform 180° phase angle differential between oneanother while maintaining a substantially uniform amplitude over saidbandwidth; a transmission line attached to said second frame andpositioned substantially around said second frame, said transmissionline comprising at least one individual segment having first and secondconductors respectively coupled to the first and second output ports ofsaid phase splitter to receive the first and second modulated carrierconstituents from said phase splitter; and a coupler attached to saidfirst frame and being positioned sufficiently near said transmissionline for establishing radio coupling therebetween so as to receive thefirst and second modulated carrier constituents being applied to said atleast one individual segment.
 16. The apparatus of claim 15 wherein saidphase splitter comprises:a dividing network comprising first and secondresistors coupled in parallel to the input port of said phase splitter;a first transmission line coupled between said first resistor and thefirst output port of said phase splitter for supplying a respectiveoutput signal having a phase angle substantially in-phase with respectto the modulated carrier, the output signal supplied by said firsttransmission line constituting the first modulated carrier constituentsupplied by said phase splitter; and a second transmission line adaptedto provide a predetermined level of inductance between said secondresistor and a predetermined electrical ground, said second transmissionline including reversing means coupled to the second output port forsupplying a respective output signal having a phase angle substantially180° out-of-phase with respect to the modulated carrier, the outputsignal supplied by said second transmission line constituting the secondmodulated carrier constituent supplied by said phase splitter.
 17. Theapparatus of claim 16 further comprising a compensating coil coupledbetween the first output port of said phase splitter and saidpredetermined electrical ground.
 18. The apparatus of claim 16 whereinsaid first and second transmission lines each comprises a respectivecoaxial line having a substantially similar electrical length relativeto one another.
 19. The apparatus of claim 18 wherein each of saidcoaxial lines comprises a flexible coaxial line wound to form asubstantially cylindrical winding.
 20. The apparatus of claim 19 whereinsaid reversing means comprises the outer shield and the center conductorof the coaxial line for said second transmission line, said centerconductor being connected to said predetermined electrical ground whilesaid outer shield is connected to the second output port of said phasesplitter to supply the second modulated carrier constituent.
 21. Theapparatus of claim 16 wherein said first and second transmission linescomprise a first printed-circuit stage including a respective pair ofsubstantially corresponding conductive strips for each of saidtransmission lines, respective ones of the conductive strip pairs beingdisposed on mutually opposite surfaces of a first substrate.
 22. Theapparatus of claim 21 wherein said first and second transmission linesfurther comprise a second printed-circuit stage including a respectivepair of substantially corresponding coils for each of said transmissionlines, each respective one of the coil pairs being coupled to arespective one of the corresponding conductive strips in said firststage and being disposed on mutually opposite surfaces of a secondsubstrate.
 23. The apparatus of claim 22 wherein each of said mutuallyopposite surfaces on said second substrate is positioned substantiallyperpendicular relative to the mutually opposite surfaces on said firstsubstrate.
 24. The apparatus of claim 23 wherein said reversing meanscomprises a feedthrough connector adapted to invert signal flow acrosseach respective one of said another pair of substantially correspondingstrips for said second transmission line.
 25. The apparatus of claim 24wherein said first and second transmission lines each has asubstantially similar electrical length relative to one another.
 26. Theapparatus of claim 16 wherein the transmission line attached to saidsecond frame further comprises additional individual segments eachhaving respective first and second conductors coupled to receiverespective first and second modulated carrier constituents, said atleast one segment and said additional segments being arranged so thatpredetermined ends of any two consecutive segments are substantiallyadjacent to one another to avoid time-delay discontinuity in themodulated carrier constituents propagating therethrough.
 27. Theapparatus of claim 26 wherein each of said individual segments comprisesa respective substantially planar transmission line and each respectivefirst and second conductor in said individuals segments is substantiallyparallel to one another.
 28. The apparatus of claim 27 wherein saidcoupler comprises a substantially planar transmission line having firstand second conductors aligned substantially parallel to one another andbeing respectively positioned substantially parallel relative to thefirst and second conductors of the respective individual segments.